The Pentagon plans to announce the repeal of its ban on openly serving transgender service members next month, US defence officials have said.

One of the US officials said on Saturday that parts of the repeal would come into effect immediately. But the plan would also direct each branch of the armed services to implement new policies affecting everything from recruiting to housing for transgender troops, the official said.

The repeal would come five years after a 2011 decision to end the US military's ban on gays and lesbians serving openly, despite fears - which proved unfounded - that such a move would be too great a burden in wartime and would undermine readiness.

The disclosure came the same week that the US army formally welcomed its new secretary, Eric Fanning, who is the first openly gay leader of a military service branch in US history.

Republican Representative Mac Thornberry, chairman of the House of Representatives Armed Services Committee, said Defence Secretary Ash Carter had not answered questions the panel had asked, including about "readiness challenges" for transgender service members.

"If reports are correct, I believe Secretary Carter has put the political agenda of a departing administration ahead of the military's readiness crisis," Thornberry said in a statement.

Supporters of transgender rights cheered the news.

Ashley Broadway-Mack, president of the American Military Partner Association, said in a statement: "Our transgender service members and their families are breathing a huge sigh of relief."

The National Centre for Transgender Equality estimated last year that 15,000 trans people served in the US military.